Hose Flow Rate Calculator
How much water actually comes out of the end of a hose decides sprinkler spacing, pool fill times and pressure-washer sizing. This hose flow rate calculator works two ways: from inside diameter and water velocity using the continuity equation Q = A × V, or from diameter, pressure and hose length using the Hazen-Williams friction equation, and it reports every result in gallons per minute and liters per minute with the full working shown.
Quick Answer
A 1/2-inch hose with water moving at 5 ft/s delivers 3.06 GPM (11.58 L/min). A 3/4-inch hose fed at 50 psi over 50 ft delivers an estimated 29.05 GPM (109.96 L/min) by the Hazen-Williams equation. Diameter is the dominant term in both modes: step up one hose size and the flow multiplies.
Key takeaways
- Velocity mode is exact physics (Q = A × V). Pressure mode is a Hazen-Williams estimate with C = 140 for smooth rubber or PVC hose.
- Flow grows with diameter to roughly the 2.6 power in the pressure mode, so 3/4-inch hose moves about three times what 1/2-inch hose moves at the same pressure and length.
- Length costs flow: doubling a 50 ft run to 100 ft cuts the pressure-mode estimate by about a third, not a half, because flow follows the square-root-like 0.54 power of the pressure gradient.
- Any calculator number is an estimate until a bucket test confirms it: time a 5-gallon fill and divide.
- Quick Answer
- How to use the hose flow rate calculator
- The formulas: continuity for velocity, Hazen-Williams for pressure
- Worked examples, one per mode
- Typical hose flow rates at 50 psi (Hazen-Williams, C = 140)
- How this page differs from the other flow-rate calculators
- What competing calculators miss
- Frequently asked questions
- Add This Calculator to Your Website
- References
How to use the hose flow rate calculator
Choose the mode that matches what you can measure. If you know the water's velocity, the first mode is exact; if you know your tap pressure and hose length, the second mode estimates the flow that friction will leave you.
Across the inner opening, in inches. Garden hoses are nominally 1/2, 5/8 or 3/4 inch.
Velocity if you have a ft/s figure, pressure + length if you have a gauge reading and a tape measure.
Both units print together with the full step-by-step working, ready to copy or share.
Two traps catch people out. First, nominal hose sizes describe the inside diameter, but cheap hoses sometimes run small, and the pressure mode punishes a small error because diameter carries an exponent of 4.87. Second, static pressure (tap closed, gauge still) is higher than the pressure available while water is moving; the pressure mode treats your entered psi as the full drop across the hose, which is the standard design assumption, and real delivery at a nozzle will be lower. If the job also needs the water sitting inside the line, for priming or winterizing, the companion hose volume calculator works out that capacity from the same diameter and length.
The formulas: continuity for velocity, Hazen-Williams for pressure
Velocity mode uses the continuity equation, Q = A × V. Pressure mode uses the Hazen-Williams friction equation solved for flow, with a roughness coefficient C = 140.
Velocity mode. Area = π × (D ÷ 2)² ÷ 144, converting square inches to square feet. Flow in cubic feet per second is area times velocity, and GPM = ft³/s × 448.831, since one cubic foot holds 7.48052 gallons and a minute holds 60 seconds. Liters per minute = GPM × 3.78541. There are no empirical constants in this mode: given a true velocity, the answer is exact, which is the same treatment of the continuity equation taught in OpenStax University Physics.
Pressure mode. The Hazen-Williams equation, the standard friction model in irrigation and fire-protection design, states the pressure drop as ΔP = 4.52 × Q^1.85 × L ÷ (C^1.85 × D^4.87). Solving for Q gives the form the calculator runs: Q = (P × C^1.85 × D^4.87 ÷ (4.52 × L))^(1 ÷ 1.85). The 4.52 constant is the psi form of the same equation published as Hf = 10.44 × L × (Q/C)^1.85 ÷ D^4.87 in feet of head in the Irrigation Energy Audit Manual used in US irrigation training. C = 140 matches published guidance for small smooth hose: irrigation references assign C = 140 to PVC in the 17 to 21 mm range, exactly garden-hose territory, and C = 150 to larger smooth plastic pipe. An older, rougher or partly scaled hose behaves like a lower C and delivers less, which is one reason the bucket test further down matters.
Worked examples, one per mode
The pre-filled velocity example returns 3.06 GPM; the pre-filled pressure example returns 29.05 GPM. Both reproduce exactly in the tool above.
Velocity: a 1/2-inch hose at 5 ft/s. Area = π × (0.5 ÷ 2)² ÷ 144 = 0.00136 ft². Flow = 0.00136 × 5 = 0.00682 ft³/s. GPM = 0.00682 × 448.831 = 3.06 GPM, or 11.58 L/min. That is a gentle hose: fine for hand watering, slow for filling.
Pressure: a 3/4-inch hose at 50 psi over 50 ft. GPM = (50 × 140^1.85 × 0.75^4.87 ÷ (4.52 × 50))^(1 ÷ 1.85) = 29.05 GPM, or 109.96 L/min. At that rate a 500-gallon tank fills in about 17 minutes with the hose running open. If your job is moving water out of something rather than into it, the same flow logic reversed is what a drain flow rate calculator applies to outlets and gravity drainage.
Typical hose flow rates at 50 psi (Hazen-Williams, C = 140)
At 50 psi supply, the pressure mode estimates 9.99 GPM for a 50 ft half-inch hose and 29.05 GPM for a 50 ft three-quarter-inch hose. Diameter, not pressure, is the lever that matters.
| Inside diameter | 25 ft | 50 ft | 100 ft |
|---|---|---|---|
| 1/2 inch | 14.53 GPM | 9.99 GPM | 6.87 GPM |
| 5/8 inch | 26.14 GPM | 17.97 GPM | 12.36 GPM |
| 3/4 inch | 42.25 GPM | 29.05 GPM | 19.97 GPM |
| 1 inch | 90.10 GPM | 61.94 GPM | 42.59 GPM |
Retail flow charts often print higher numbers than this table: Hoselink's guide lists 38 GPM for a 50 ft, 3/4-inch hose at 45 psi, and Heartland Hoses lists 36 GPM at 40 psi. Those charts describe near-open discharge with smooth new hose and little residual pressure requirement, while Hazen-Williams at C = 140 is a design estimate that keeps a safety margin. Your own hose will land where its age, fittings and nozzle put it, which is why both guides, and this page, point you back to a timed bucket fill as the deciding measurement. Where a system also tracks pressure loss across a network rather than one hose, a flow rate pressure calculator covers that pipe-network side of the same physics.
How this page differs from the other flow-rate calculators
This is the hose-specific tool: its inputs are a hose's inside diameter and either the water velocity or the supply pressure and hose length. The site's other flow tools answer different questions.
A water flow rate calculator in the pipe sense works on fixed plumbing runs; a volumetric flow rate calculator converts between flow units and cross-sections for any conduit; a mass flow rate calculator multiplies by density to get kilograms per second, which matters for process fluids rather than garden water; pool and oxygen flow tools are built around their own equipment ratings and turnover targets; and a waterfall flow calculator estimates flow over a weir or spill edge, a free-surface problem with different maths entirely. If your conduit is a hose and your known quantities are diameter, velocity, pressure and length, you are in the right place; if you are sizing a pump circuit or a weir, those sibling pages fit better.
What competing calculators miss
Most hose calculators pick one method and hide its assumptions. Several also print numbers that fail a basic reality check against published hose charts.
- AreaCalculators: pressure-mode only, using an empirical power formula. Its own worked example for this page's default inputs (0.75 in, 50 psi, 50 ft) claims 15.2 GPM, but substituting its numbers into its printed formula gives about 44 GPM, so the page's formula and its examples disagree with each other. No velocity mode, no metric output.
- CalculatorsHub: built on the fire-nozzle equation Q = 29.7 × d² × √P, which answers a different question (flow through a smooth-bore nozzle at nozzle pressure). Its friction-loss example subtracts a 66 psi loss from a 50 psi supply and lands on negative pressure without flagging that the setup is impossible as stated.
- Hoselink and Heartland Hoses: genuinely useful measured flow charts and bucket-test advice, but no calculator: you interpolate between their tabulated diameters, lengths and pressures and cannot run your own combination.
- Firgelli's engineering calculators: proper Darcy-Weisbach pressure-drop work, but aimed at hydraulic-oil circuits with viscosity inputs; oversized and off-target for a water hose question.
- The gap this page fills: both standard methods on one page, the exact continuity mode and a Hazen-Williams pressure mode with its C factor stated in the open, GPM and L/min together, step-by-step working for every result, and an honest pointer to the bucket test when an estimate is not enough.
Frequently asked questions
Most residential garden hoses deliver somewhere between about 5 and 30 GPM depending on diameter, pressure and length: a 50 ft half-inch hose at 50 psi estimates at 9.99 GPM in the pressure mode above, while a 50 ft three-quarter-inch hose at the same pressure estimates at 29.05 GPM. If a bucket test shows under 3 GPM at an outdoor spigot, something is restricting the line.
Use velocity mode when you know the water speed in ft/s: it is the continuity equation Q = A times V with no empirical constants, so the result is exact for that velocity. Use pressure mode when you know your supply psi and hose length but not the velocity; it estimates flow with the Hazen-Williams friction equation.
Run the bucket test: time how long the open hose takes to fill a 5-gallon bucket, then divide 5 by the minutes. A 36-second fill is 5 divided by 0.6 minutes, about 8.3 GPM. Run it three times and average. The bucket test beats every calculator because it captures your real pressure, fittings and hose condition.
Friction between the moving water and the hose wall converts pressure into heat all along the run. In Hazen-Williams terms the pressure drop grows in direct proportion to length, so at fixed supply pressure a longer hose has a weaker pressure gradient driving the flow, and flow falls with the 0.54 power of that gradient: doubling the length cuts flow by about a third.
C is the Hazen-Williams roughness coefficient: higher means a smoother bore and less friction. Irrigation references assign C = 140 to smooth plastic pipe in the 17 to 21 mm range, which is garden-hose diameter territory, and 150 to larger smooth plastic pipe. This calculator fixes C = 140 for smooth rubber or PVC hose; an old, rough or scaled hose behaves like a lower C and will deliver less than the estimate.
Because the old pressure formula was wrong. It divided the hose's cross-sectional area times pressure by length times 2.31, which returned 0.19 GPM for a 3/4-inch hose at 50 psi over 50 ft, roughly 150 times less than such a hose actually delivers. The mode now uses the Hazen-Williams equation, the standard friction model for water in pipes and hoses, and the same inputs return 29.05 GPM.
No. Both modes assume a straight, unobstructed hose discharging freely. A spray nozzle, kink, partly closed valve or long uphill run all reduce real flow below the estimate, sometimes by half. Treat the result as the hose's open-flow figure and measure with a bucket when the end fitting matters.
For rough planning, yes; for design or safety decisions, no. The pressure mode is a Hazen-Williams estimate with a fixed C = 140, while fire-hose work uses hose-specific friction-loss coefficients and nozzle pressures, and life-safety design belongs to the NFPA methods and a qualified engineer. A pressure washer's supply hose also has to meet the machine's minimum inlet flow, which the manufacturer's manual states.
Add This Calculator to Your Website
Embed this calculator on your own site with the code below. Pick a size to preview it live, then copy the code.
Powered by Calculator Zilo
References
- University of Florida IFAS Extension / AgroClimate. Irrigation Energy Audit Manual, Equation 3.2 (Hazen-Williams friction loss) and Table 3.4 (C values). Accessed October 22, 2026.
- Canute LLP (CanuteSoft). The Hazen-Williams Formula for Use in Fire Sprinkler Systems. Accessed October 22, 2026.
- Indian Agricultural Research Institute thesis repository (KrishiKosh). Design of Semi-Permanent Sprinkler Irrigation System and Its Performance (Hazen-Williams C values for PVC by diameter). Accessed October 22, 2026.
- OpenStax, University Physics Volume 1 (hosted by Vaia). Chapter 14, Problem 126: volume flow rate and the continuity equation in a garden hose. Accessed October 22, 2026.
- Hoselink. Garden Hose Flow Rate: GPM Explained and How to Test It. Accessed October 22, 2026.
- Heartland Hoses. What is Water Hose Flow Rate? Measurement Guide With Chart. Accessed October 22, 2026.